Drug-coated stents can improve the overall effectiveness of angioplasty and stenotic procedures performed on the cardiovascular system and other vessels within the body by delivering potent therapeutic compounds at the point of infarction. Drugs such as anti-inflammatants and anti-thrombogenics may be dispersed within the drug-polymer coating and released gradually after insertion and deployment of the stent. These drugs and coatings can reduce the trauma to the local tissue bed, aid in the healing process, and significantly reduce the narrowing or constriction of the blood vessel that can reoccur where the stent is placed.
The conventional approach to drug-coated stents incorporates the therapeutic agent into a polymeric solution and then coats the stent, such as described in “Bioactive Agent Release Coating” by Chudzik et al., U.S. Pat. No. 6,214,901, issued Apr. 10, 2001. The ideal coating must be able to adhere strongly to the metal stent framework both before and after expansion of the stent, and be able to control release the drug at sufficient therapeutic levels for several days, weeks or longer. Unfortunately, some drug polymers do not provide the mechanical flexibility necessary to be effectively used on a stent. A stent may be deployed by self-expansion or balloon expansion, accompanied by a high level of bending at portions of the stent framework, which can cause cracking, flaking, peeling, or delaminating of many candidate drug polymers while the stent diameter is increased by threefold or more during expansion. The coating must also be thin enough as not to significantly increase the profile of the stent. These types of coated stents allow drugs to diffuse to the vessel walls as well as into the blood stream through the lumen. Bioactive agents diffused into the vessel wall increase efficacy and patent pharmaceutical effects at the point of need, whereas drugs diffused into the blood stream may be quickly flushed away and become ineffective, thereby requiring thicker coatings or a greater amount of drugs to be loaded into the stent coating.
A possible alternative to a coated stent is a stent containing reservoirs that are loaded with a drug, as discussed by Wright et al., in “Modified Stent Useful for Delivery of Drugs Along Stent Strut,” U.S. Pat. No. 6,273,913, issued Aug. 14, 2001; and Wright et al., in “Stent with Therapeutically Active Dosage of Rapamycin Coated Thereon,” US patent publication US 2001/0027340, published Oct. 4, 2001. This type of system seems to work well if there is only one drug to load and if the reservoirs are small. However, when the reservoirs are large such as with long channels, repeated loadings of a drug by dipping would pose some challenging problems due to excessive build-up of a drug polymer on the stent framework.
Wright et al. in U.S. Pat. No. 6,273,913, describes the delivery of rapamyacin from an intravascular stent and directly from micropores formed in the stent body to inhibit neointinal tissue proliferation and restenosis. The stent, which has been modified to contain micropores, is dipped into a solution of rapamycin and an organic solvent, and the solution is allowed to permeate into the micropores. After the solvent has been allowed to dry, a polymer layer may be applied as an outer layer for a controlled release of the drug.
U.S. Pat. No. 5,843,172 by Yan, which is entitled “Porous Medicated Stent”, discloses a metallic stent that has a plurality of pores in the metal that are loaded with medication. The drug loaded into the pores is a first medication, and an outer layer or coating may contain a second medication. The porous cavities of the stent can be formed by sintering the stent material from metallic particles, filaments, fibers, wires or other materials such as sheets of sintered materials.
Leone et al. in U.S. Pat. No. 5,891,108 entitled “Drug Delivery Stent” describes a retrievable drug delivery stent, which is made of a hollow tubular wire. The tubular wire or tubing has holes in its body for delivering a liquid solution or drug to a stenotic lesion. Brown et al. in “Directional Drug Delivery Stent and Method of Use,” U.S. Pat. No. 6,071,305 issued Jun. 6, 2000, discloses a tube with an eccentric inner diameter and holes or channels along the periphery that house drugs and can deliver them preferentially to one side of the tube. Scheerder et al. in US patent publication US 2002/0007209, discloses a series of holes or perforations cut into the struts on a stent that are able to house therapeutic agents for local delivery.
It is desirable to have a medicated stent that can be tailored to provide a desired elution rate for one or more drugs and to provide sufficient quantities of bioactive agents without compromising the mechanics of the stent during deployment and use. It would be beneficial to have a drug-polymer system that can be tailored to accommodate a variety of drugs for controlled time delivery, while maintaining mechanical integrity during stent deployment. Furthermore, it would be beneficial to provide a drug-polymer stent with phased delivery of drugs in effective quantities.
It is an object of this invention, therefore, to provide a framework and structure for effective, controlled delivery of suitable quantities of pharmaceutical agents from medicated stents. It is a further object to provide a system and method for treating heart disease and other vascular conditions, to provide methods of manufacturing drug-polymer stents, and to overcome the deficiencies and limitations described above.